Implement EmailBlackList (#5109)

* Implement BlacklistedEmailDomain

* Use Faker::Internet.domain_name

* Remove note column

* Add frozen_string_literal comment

* Delete unnecessary codes

* Sort alphabetically

* Change of wording

* Rename BlacklistedEmailDomain to EmailDomainBlock

app/views/admin/email_domain_blocks/index.html.haml

@@ -0,0 +1,13 @@
+- content_for :page_title do
+  = t('admin.email_domain_blocks.title')
+
+%table.table
+  %thead
+    %tr
+      %th= t('admin.email_domain_blocks.domain')
+      %th
+  %tbody
+    = render @email_domain_blocks
+
+= paginate @email_domain_blocks
+= link_to t('admin.email_domain_blocks.add_new'), new_admin_email_domain_block_path, class: 'button'